The present invention relates to a display device such as a fluorescent display device using a cathode filament; and, more particularly to a cathode filament serving as an electron source for the display device.
FIGS. 10A and 10B show schematic internal structures of conventional display devices 800 and 850, respectively. Referring to FIG. 10A, the display device 800 includes a glass substrate 81, a filament 84, a filament support 82 and an anchor 83 for the filament 84. While one end of the filament 84 is fixed to a support member 821 of the filament support 82, the other end of the filament 84 is fixed to a support member 831 of the anchor 83. The height of the filament support 82 and that of the anchor 83 define the height (i.e., a distance between the substrate 81 and top end thereof) of the filament 84 (e.g., see, Japanese utility model laid open publication No. 61-7856).
The support member 831 of the anchor 83 is formed as a plate spring structure. A preset tension force is applied to the filament 84 to prevent the filament from hanging down due to the thermal expansion thereof. Accordingly, the plate spring structure of the support member 831 should be fabricated so that a uniform tension force is applied to the filament 84. Further, the support member 831 should be fabricated with high precision since the support member 831 should fixedly support the filament 84 and maintain the height of the filament 84 at a preset level. The anchor 83 is of a complex structure, requiring a fabrication with high accuracy, and therefore, its fabrication is not easy and the cost thereof is expensive. In addition, it is not easy to make the anchor 83 of a small size, thereby rendering the fabrication of a thin and small display device difficult. FIG. 10B illustrates a schematic internal structure of a conventional display devices 850 which does not use an anchor. Like reference numerals represent like parts in FIGS. 10A and 10B.
Referring to FIG. 10B, the display device 850 includes a glass substrate 81, a left filament support 82, a right filament support 82xe2x80x2 and a filament having a coiled portion 842 and a linear portion 841. The filament supports 82 and 82xe2x80x2 are fixed at a left and right end portion on top of the substrate 81, respectively. While the left end of the coiled portion 842 is fixed at a support member 821 of the left filament support 82, the right end of the linear portion 841 is fixed at a support member 821xe2x80x2 of the right filament support 82xe2x80x2. The coiled portion 842 applies a tension force on the linear portion 841, thereby functioning similar to the anchor 83 in the device 800 shown in FIG. 10A (e.g., see, Japanese utility model laid open publication No. 61-7856).
The device 850 solves the problem of the anchor 83 as shown in FIG. 10A but entails another problem in that a temperature of the coiled portion 842 becomes higher than that of the linear portion 841 during the operation of the display device 850. Namely, for example, during normal turning-on period of the display device 850, the temperature of the coiled portion 842 reaches to about 800xc2x0 C. while that of the linear portion 841 approaches to about 600xc2x0 C. Under this condition, the coiled portion 842 emits red light to thereby prevent a normal display operation thereof.
In a manufacturing process of a conventional display device, in order to activate the filament, a flushing is performed at a high voltage. During the flushing, the temperature of the coiled portion 842 reaches to about 1500xc2x0 C. to 2000xc2x0 C. while that of the linear portion 841 reaches to 1000xc2x0 C. As a result, electron emitting source material, e.g., a carbonate, coated on the coiled portion 842 is decomposed and flies around thereby contaminate fluorescent material deposited on an anode. This prevents the display device from operating normally.
It is, therefore, an object of the present invention to provide a simple and inexpensive display device of high display quality by employing a filament free from above-mentioned problems, i.e., display quality degradation due to red light emission from the coiled portion and contamination of fluorescent material deposited on the anode due to flight of carbonate of a coiled portion, originated from an excessively high temperature of the coiled portion of the filament.
The display device of the present invention overcomes the above-mentioned problems of the conventional display device by adopting a cathode filament having a coiled portion and a linear portion and applying a tension force with the coiled portion and providing electrons only to the linear portion of the filament.
In accordance with a preferred embodiment of the present invention, there is provided a display device including: a cathode filament containing a coiled portion and a linear portion thereof; and a power feeding member, wherein an end of the coiled portion is fixed either to a substrate made of an insulating material or to an insulated support, the power feeding member being installed to contact with the linear portion of the cathode filament.
In accordance with another preferred embodiment of the present invention, there is provided a display device including: a cathode filament containing a coiled portion and a linear portion thereof; and a power feeding wiring for feeding power to the cathode filament, wherein an end of the coiled portion is fixed on either the power feeding wiring or a support member fixed on the power feeding wiring, the coiled portion being insulated.
In accordance with yet another preferred embodiment of the present invention, there is provided a display device including: an anode substrate; a back substrate having either a transparent conductor film or a control electrode formed thereon; a cathode filament installed between the anode substrate and the back substrate, the cathode filament having a coiled portion and a linear portion thereof; and a plurality of spacers fixed to either the transparent conductor film or the control electrode of the back substrate, wherein an end of the coiled portion is fixed either on an insulated support fixed on one of the anode substrate and the back substrate or on one of the anode substrate and the back substrate, a power feeding member being installed to contact with the linear portion of the cathode filament and the substrate on which the end of the coiled portion is fixed being made of insulating material.
In accordance with still yet another preferred embodiment of the present invention, there is provided a display device including: an anode substrate; a back substrate having either a transparent conductor film or a control electrode formed thereon; a cathode filament installed between the anode substrate and the back substrate, the cathode filament having a coiled portion and a linear portion thereof; and a plurality of spacers fixed to either the transparent conductor film or the control electrode of the back substrate, wherein an end of the coiled portion is fixed on either a support member fixed on a power feeding wiring of the cathode filament or the power feeding wiring, the coiled portion being insulated.